The young Sigmund Freud started his career as a scientific researcher by looking for testicles in the body of the eel. This is harder than it sounds. Eels caught in fresh water have scarcely developed genitals because they don't grow till they're needed, and the eels, as Freud didn't know, breed 3,000 miles away from Trieste, where he studied them. His identification of the tissues that would become testicles was tentative, and not accepted for some time. He went off to spend the rest of his life in the more rewarding study of balls in the human brain.

Slimy, inexhaustible and almost impossible to kill, the eel returned to obscurity. It feeds and travels mysteriously, by night; for centuries its sex life was a perfect mystery. Alone among fish, it undergoes a metamorphosis as it grows, changing entirely from a flat, transparent larva, shaped like a miniature willow leaf, into an elver, which looks like a skinny bean sprout. In that form it struggles up rivers in millions, until it finds a place to settle, where it darkens, swells, and becomes the black, muscular and sinister beast of legend and fishermen's tales.

Few people will eat it at all, but those who do, love it to excess, and catch it by any means possible and some impossible: the Roman writer who first described fly fishing in the second century AD also described a technique of eel fishing using lamb's intestines as both bait and tackle. The trick was to stick a hollow reed in one end of the intestine, dangle the other in the water, and when an eel started to suck on it, to blow like hell so that the eel, unable to release the inflated tube, would choke to death.

It seems an elaborate way to kill the beast, but eels are incredibly tough. The first - and last - eel I caught on rod and line was still writhing slowly 10 minutes after its head had been cut off. The only completely painless method of killing them may be the American one mentioned in Richard Schweid's book: you put them in a dustbin half full of water; dump "half a can of Prince Albert tobacco" on top; put a towel over the dustbin to seal all in. "You'd put the tobacco in and they'd quiver, and just go stiff. We'd wait 15 minutes and take them out and skin them."

It must have seemed a perfect proposition for publishers, dazzled by the success of Mark Kurlansky's Cod. So now we have two books on eels, covering very much the same ground, which might serve as set books in any course teaching the differences between English and American journalism. They don't entirely conform to stereotype: American books are meant to be the inflated ones, but in this case it's Fort's that seems to be about a quarter padding: very high-class fluff, admittedly; but there is a limit to the interesting things that can be said about the eel and he has rather exceeded it. This sense of disappointment arises partly because the good bits are so very good that the merely competent parts of the book stand out.

The strength of Fort's book arises from the fact that he's a fisherman, and writes like one. He approaches the eel as a mystery, and he loves the places where it is found. His descriptions of the desolate cold marshes and lagoons where they are trapped are really fine. He has also done his research about the natural history of the beast, and how it was discovered.

In 1922 a Danish scientist, Johan Schmidt, who had devoted nearly 15 years to the problem, announced he had found the answer. By backbreaking, monotonous and unrewarding work, looking for creatures 7mm long by dipping nets into the middle of the Atlantic Ocean, he had established they breed deep in the Sargasso Sea. To this day, no one has seen it happen; and while everyone now believes the theory, Fort shows that Schmidt did pretty up his data to strengthen his argument about where exactly in the Sargasso Sea the breeding grounds lie.

Schweid's book has much the same stories and often features the same people. The world of professional eel fishing is small. Both men travel to Lough Neagh to interview the same priest. Both men talk to the same eel wholesaler in North Carolina; but Schweid has a better grasp of the economics of the business. Still, the American is never afraid of the bathetic quote. The people he interviews are constantly leaning towards the reader, in the manner of a pub bore, and giving off little snippets of establishing dialogue.

Of course in the real world, people do talk like that, which is why one would much rather be out on the water with Tom Fort.